From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 313FD3FC1 for ; Tue, 24 Aug 2021 06:55:49 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 77C0D68AFE; Tue, 24 Aug 2021 08:55:46 +0200 (CEST) Date: Tue, 24 Aug 2021 08:55:46 +0200 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , Vishal Verma , Dave Jiang , Mike Snitzer , Matthew Wilcox , linux-xfs , Linux NVDIMM , linux-fsdevel , linux-ext4 Subject: Re: [PATCH 1/9] fsdax: improve the FS_DAX Kconfig description and help text Message-ID: <20210824065546.GA24465@lst.de> References: <20210823123516.969486-1-hch@lst.de> <20210823123516.969486-2-hch@lst.de> Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) On Mon, Aug 23, 2021 at 11:45:52AM -0700, Dan Williams wrote: > On Mon, Aug 23, 2021 at 5:37 AM Christoph Hellwig wrote: > > > > Rename the main option text to clarify it is for file system access, > > and add a bit of text that explains how to actually switch a nvdimm > > to a fsdax capable state. > > > > Looks good, nice improvement. A couple suggestions below. Does this looks ok? --- >From c69617137a1e6b67122c871c946e7aa00b03978b Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 23 Aug 2021 10:57:37 +0200 Subject: fsdax: improve the FS_DAX Kconfig description and help text Rename the main option text to clarify it is for file system access, and add a bit of text that explains how to actually switch a nvdimm to a fsdax capable state. Signed-off-by: Christoph Hellwig --- fs/Kconfig | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/fs/Kconfig b/fs/Kconfig index a7749c126b8e..bd21535a7620 100644 --- a/fs/Kconfig +++ b/fs/Kconfig @@ -43,7 +43,7 @@ source "fs/f2fs/Kconfig" source "fs/zonefs/Kconfig" config FS_DAX - bool "Direct Access (DAX) support" + bool "File system based Direct Access (DAX) support" depends on MMU depends on !(ARM || MIPS || SPARC) select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED) @@ -53,8 +53,23 @@ config FS_DAX Direct Access (DAX) can be used on memory-backed block devices. If the block device supports DAX and the filesystem supports DAX, then you can avoid using the pagecache to buffer I/Os. Turning - on this option will compile in support for DAX; you will need to - mount the filesystem using the -o dax option. + on this option will compile in support for DAX. + + For a DAX device to support file system access it needs to have + struct pages. For the nfit based NVDIMMs this can be enabled + using the ndctl utility: + + # ndctl create-namespace --force --reconfig=namespace0.0 \ + --mode=fsdax --map=mem + + See the 'create-namespace' man page for details on the overhead of + --map=mem: + https://docs.pmem.io/ndctl-user-guide/ndctl-man-pages/ndctl-create-namespace + + For ndctl to work CONFIG_DEV_DAX needs to be enabled as well. For most + file systems DAX support needs to be manually enabled globally or + per-inode using a mount option as well. See the file documentation in + Documentation/filesystems/dax.rst for details. If you do not have a block device that is capable of using this, or if unsure, say N. Saying Y will increase the size of the kernel -- 2.30.2